Method for coating fasteners

ABSTRACT

A method and apparatus for coating a fastener with head and shank portions is disclosed. The invention includes the steps of and apparatus for transferring the fasteners from a feed mechanism such that the fasteners are positioned for coating. The fasteners are then conveyed through a plurality of operating stations, beginning with a heating station where the shank portions of the fasteners are heated. Subsequently, at a material applying station, a coating material is applied to the heated shank portions. A preferred embodiment of the method and apparatus of the present invention includes using a magnetic holder to carry the fasteners horizontally by their head portions, heating the shank portion to a temperature above the melting point of the applied material and applying the material to the heated shank portion to form a coating thereon. The magnetic holders are part of an endless traveling belt that rotates continually. The fastener carriers have teeth that engage a rack to rotate the fasteners. A conveyor provides added air cooling for the coated fasteners, which can continue to be rotated. Also disclosed is a transfer wheel with two sets of notches that is synchronously coupled to the traveling belt for placing and aligning fasteners on the belt for coating.

TECHNICAL FIELD OF THE INVENTION

This invention relates to an apparatus and method for coating fasteners,and more particularly to an improved method and apparatus for coatingfasteners with shank and head portions.

BACKGROUND OF THE INVENTION

Numerous methods and devices have been employed in the past for coatingfasteners. Some of these methods and devices are useful in coatingcertain types of fasteners, but are not as versatile in coating othertypes of fasteners.

Examples of such methods and devices include U.S. Pat. Nos. 3,452,714 inthe names of G. F. C. Burke, Richard J. Duffy et al.; 4,120,993 toRichard J. Duffy et al.; and Re. No. 28,812 to Richard J. Duffy, one ofthe present inventors. The methods and devices disclosed in these UnitedStates Patents provide for the coating of fasteners in which the shankportion of the fastener depends below a pair of traveling belts. Thesefasteners are supported on the belts at their head portion. The methodsand apparatus of the previously described patents do not provide theability to precisely control the linear speed and rotation of thefasteners during the coating process. Also, it would be advantageous toprovide a method and apparatus which would automatically and rapidlycoat a wide variety of different fastener configurations and which maybe adapted for use with a variety of different types of coatings.

It would also be advantageous to provide a method and apparatus whichaccommodates a variety of different fastener configurations and sizesand which could be quickly and easily adapted for coating suchfasteners. In addition, it is desirable to provide a method andapparatus which has the versatility to coat a specified portion of thethreads of the fastener, as well as the complete threaded area, andfurther, a method and apparatus which may coat only a specific portionof the radial distances about the threaded surface of the fastener.Furthermore, it would be advantageous to provide a method and apparatuswhich provides the ability to precisely control the linear speed androtation of the fasteners to be processed.

The solutions to some of these problems have been disclosed in theapplication, Ser. No. 070,416, filed Jul. 7, 1987, now U.S. Pat. No.4,842,890, the disclosure of which is incorporated herein by reference.Improvements, however, are still desirable to increase the speed andefficiency of the apparatus and method, allow for faster and easieradaptation to fasteners of different configurations and sizes, create asmoother and more even coating of material, allow the use of differenttypes of coating, and prevent clogging of the coating nozzle.

SUMMARY OF THE INVENTION

The present invention is an apparatus that applies a coating tofasteners. Prior to having the coating applied by the appropriate means,the fasteners are passed through a heating means such as an inductioncoil. The fasteners travel through the heating means and by the coatingmeans on an advancing means such as a traveling belt. Fasteners aredirected onto the advancing means by a transferring means such as atransfer wheel, that receives aligned fasteners in a continuous supply.

In a preferred embodiment the traveling belt has equally spaced,removable, magnetic carrying members that hold the fastener heads. Anevenly applied coating to the fastener is assured by a means forcontrolling the degree of surface coating on the fasteners, which canbe, among other arrangements, a rack of teeth engageable withcomplementary teeth on the carrying members to provide for theirrotation. Full rotation of the fasteners ensures an even, typically 360degree coating of material, while a less than full rotation can limitthe application of the coating to less than 360 degrees if the coatingis only applied from one direction. Rotation of the fasteners after theapplication of the coating is complete improves the smoothness andevenness of the coating, especially with liquid coatings. Suchadditional rotation also facilitates cooling.

Another preferred feature of the invention is the transfer wheel thatplaces the fastener on the traveling belt. The wheel has two sets ofnotches, one that carries the fasteners and another that interacts witha biased striking element to move the fasteners from the wheel tocarrying members on the belt. The transfer wheel and the belt are drivenby the same motor and pulley system, so that the wheel is easilyadjusted to accommodate different configurations and sizes of fasteners.

In another preferred embodiment, the fasteners are moved from thetraveling belt to a cooling conveyor. The conveyor belt is preferably anair permeable mesh, so that air curtains or air knives can be placedaround the conveyor to more quickly cool the coated fastener.

Another desirable feature of the apparatus of the present invention is aspray nozzle that is particularly effective with powder coatings. Aninterior surface disburses the material, whose velocity is increased bya secondary source of air supplied at the top of the nozzle. Flatteningthe outlet of the nozzle provides additional control to theapplicability of the coating, as does making the nozzle rotatablyadjustable to accommodate various coating lengths.

Other features include a cover made of materials sold under thetrademark TEFLON® polytetrafluoroethylene for the magnetic carryingmember to protect the magnet end from becoming coated when coating isapplied to the entire fastener. The magnetic insert of the carryingmember can also be made to be removable.

A process using the described features is also provided.

DESCRIPTION OF THE DRAWINGS

The novel features which are characteristic of the invention are setforth in the appended claims. The invention itself, however, togetherwith further objects and attendant advantages thereof, will be bestunderstood by reference to the following description taken in connectionwith the accompanying drawings, in which:

FIG. 1 is a schematic of the process and device practicing the presentinvention;

FIG. 2 is a perspective view of an apparatus practicing the presentinvention;

FIG. 3 is a perspective view of portions of the aligning means, transferwheel and traveling belt of the apparatus of FIG. 1;

FIG. 4 is a perspective view of the geared ends of the carrying membersof the apparatus of FIG. 1 as they engage the rack of teeth forrotation;

FIG. 5 is a perspective view of the transfer wheel of the apparatus ofFIG. 1 with the striking member biased away from a fastener and thetraveling belt;

FIG. 6 is a perspective view of the striking member of the apparatus ofFIG. 1 after it has been biased into one of the second set of notches totransfer the fastener to the traveling belt; and

FIG. 7 is an exploded view of an applicator nozzle with a flattenedoutlet shown in phantom.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic drawing that outlines the general features of themethod and apparatus of the present invention. A general descriptionwill be followed by a more specific one. A continuous supply offasteners is provided as fasteners are transferred from a bulk storagedevice 12 to a conventional bucket elevator and a conveyor 14, whichdumps the fasteners into a vibrating distribution and orientation device16, such as one commercially available from Moorfeed Corp. The fastenersemerge from the vibratory bowl onto a dispensing track 18, at which timethe heads and shanks of all fasteners are aligned in the same direction.Preferably the shanks are parallel to the floor.

The fasteners then slide into notches 22 (FIG. 5 and 6) spaced equallyaround the perimeter of a transfer wheel 20. Transfer wheel 20 is drivenby a 5 horsepower DC motor that, by way of belts and pulleys, alsodrives traveling belt means such as a traveling belt 50. A strikingassembly (shown in FIGS. 5 and 6) displaces the fasteners ontomagnetized carrying members 52 (FIG. 2) of the traveling belt. Thefasteners are passed through a heating station such as an induction coil65 to heat the surfaceof the fastener to a temperature at which thecoating to be applied will adhere. In the case of power sold under thetrademark TEFLON®, approximately 700°-900° Fahrenheit is the preferredtemperature range. Still more preferable is approximately 775°-825°Fahrenheit. This can be achieved by a variety of methods. One suchmethod is induction heating, utilizing a 75 kilowatts--10k Hz powersupply and an appropriate induction coil. This lowfrequency providesdeeper current penetration for heating of the fastener at reduced costs.The power to the coil can, of course, be varied by the appropriatecontrols known to those in the art. As one skilled in the art mayappreciate, a variety of power supplies with various power ratingsandoperating frequencies can be used, depending on the type and size offasteners to be processed.

After the fasteners pass through the induction coil, a rack of teeth 102engages and begins to rotate the fasteners, which then pass under adevicethat dispenses the material used for forming the coating on thefasteners. Powdered materials for forming such coatings are supplied ina manner described in part in the previously incorporated references,specifically through a dispensing nozzle 70 onto the fasteners. Excesspowder is salvaged by a vacuum pick-up 72 on the other side of nozzle70. To ensure an even coating, the fasteners can be further turnedsubsequent to the application process. Depending upon the necessaryparameters of the coating process, the rack of teeth can be used torotate the fasteners at any position in the heating, coating, and/orcooling steps of the process.

A cooling conveyor 120 is provided to further cool the fasteners beforethey are immersed in a final bath for cooling and/or the application ofa rust inhibitor. The conveyor 120 can be operated in ambientconditions, orit can be used in association with devices such as airamplifiers or air knives 125. Additional cooling may be utilized tolower the temperature ofthe fasteners below the boiling point of thefinal bath. In addition, when a coating sold under the trademark TEFLON®is used, gradual cooling ispreferred to allow the coating sold under thetrademark TEFLON® time toset. Otherwise rapid cooling may reduce thequality of the bond between thefastener and the coating, resulting in alower level of adhesion.

FIG. 2 depicts in detail many of the aspects of the present invention. Aportion of the means for providing a continuous and aligned supply offasteners is shown generally as 10, and incorporated in the apparatus ofFIG. 1 including bulk storage device 12, bucket elevator and conveyor14, vibrating bowl 16, and dispensing track 18. These are allcommercially available and known to those of ordinary skill in the art.

As the fasteners 11 come off the dispensing track 18, they are alignedpreferably so that the shanks are horizontal and the heads are vertical.The shanks slide into a first set of notches 22 on transfer wheel 20.Transfer wheel 20 can be directly turned by an output shaft connected toadirect current (D.C.) motor (not shown, see U.S. patent applicationSer. No. 070,416) or by a belt 24 and pulleys 26 and 27. If the motor isnot connected directly to transfer wheel 20, then it drives sprocket 32which turns traveling belt 50. By means of the belts and pulleys,preferably, one motor synchronously turns the transfer wheel 20 andtraveling belt 50.In this way, the traveling belt and the transfer wheelcan preferably be adjusted into alignment quickly to accommodate avariety of fastener sizes.

The principal features of the structure and operation of the transferwheel20 are depicted in FIGS. 3, 5, and 6. As noted earlier, a head 29of striking element 28 contacts fastener 11 at the moment the fasteneris aligned with a magnetic carrying member 52. The fastener 11 is thenheld by the magnetic force of carrying member 52 as the fastener islifted out of the notch by the motion of the belt 50 and associatedcarrying member 52.

Particularly as shown in FIGS. 5 and 6, wheel 20 also has a second setof notches 34 on the side of the wheel which preferably cooperate withstriking element 28 biased by spring 36. The notches 34 are preferablytrapezoidal in shape, with striking element 28 biased to move into thenotch. As the wheel rotates in the direction of Arrow A, angled side 34Bworks against the biasing force (Arrow B) exerted by spring 36 to movestriking element 28 upwardly from lower notch surface 34C to flat uppernotch surface 34E. As the wheel continues to rotate, surface 34E slidesagainst striking element 28 until the edge of the striking elementcompletely clears the upper surface 34E and the edge of vertical side34D.Spring 36 then pushes element 28 completely into the next notch.Head 29 ofstriking element 28 then engages fastener 11 moving it intocontact with magnetic carrying member 52.

Traveling belt 50 is preferably an endless chain of links 54 that isdrivenby sprocket 32 and supported by a second sprocket 33 (FIG. 2).Although other types of carrying assemblies such as belts, wire, cordsand the likecan also be used. Various structures, such as connectors 56,can be used toconnect carrying members 52 to chain links 54 (FIG. 4).The carrying members 52 are preferably hollow, so that permanent magnets60 can be inserted and held in place by set screw 62, thus forming amagnetic holding means (FIGS. 5 and 6). This configuration has theadvantage of securing the fastener in correct position for coating. Thecarrying members are preferably aluminum shells, while the inserts arepreferably ALNICO V heat resistant permanent magnetic assemblies.

Fasteners 11 are moved through a heating station, such as induction coil65, and then under a means for applying the coating material, such asnozzle 70. A means for removing excess coating material, such as vacuumpick-up 72, is associated with the application nozzle. A drip pan orotherdrainage device can be used if the coating material is a liquid.The coating material, preferably a powder material, is applied from asource (not shown) that preferably fluidizes the powder and conveys itunder pressure to the nozzle 70. Other embodiments, however, are alsocontemplated where a powder coating material may be provided by avibratory gravity feed device, or a liquid coating material is providedunder pressure or gravity, depending upon the physical characteristicsof the material. Electromechanical and hydraulic control of the coatingapplication, belt speed, heating element, and other devices withvariable characteristics can be exercised by various means known tothose of skill in the art.

As shown in FIG. 4, carrying members 52 are rotated by an assembly 100for controlling the degree of surface coating on the fasteners. Assembly100, as included in the apparatus of FIG. 1, may include a rack of teeth102 engageable with rotating pinions 104 on the ends of rotatingcarrying members 52. The first portion 106 of rack 102 (with referenceto the motion of belt 50, as signified by Arrow B) is separate from theremainderof rack 102 and pivotable about spindle 108. This facilitatesproper and efficient engagement of the pinions 104 with teeth 102.Without the pivoting capability, the teeth of the two engaging objectsmight not mesh properly. A biasing member (not shown) is located betweenlower plate 110 and first portion 106 to create a biasing force as shownby Arrow C. Any one of a number of different types of springs, attachedto spindle 108 or under first portion 106, can provide the necessaryforce.

Typically controlling means 100 will rotate the fasteners through 360°during the application of the coating material, although specificlengths of rack 102 can result in rotations more or less than 360° toprovide coating of selected circumferential portions of each fastener11. When rack 102 is removed, the fasteners typically are coated on "oneside," i.e., 180° degrees of the shank. Rack 102 canbe extended ineither or both directions from the coating application station. Theextension of rack 102 beyond the coating station enables the continuingrotation of the fastener for a period of time limited only by the lengthof belt 50 and teeth 102. The same technique is also effective when aliquid coating, such as the liquid coating sold by Nylok FastenerCorporation under the trademark PRECOTE®, is applied. If thefastenersare sufficiently rotated, the need is eliminated to removedrops of liquid that otherwise form on the bottom of the fastener. Suchremoval would typically be performed by a stationary brush locatedadjacent to the belt.

When rotation of the fastener is no longer necessary, the belt 50 can bemoved by stationary discharge cam 115, which contacts the heads of eachpassing fastener 11 and causes each fastener to slide off the end ofmagnet 60, down slide 117, and onto cooling conveyor 120. Coolingconveyor120 preferably includes a mesh belt 122 that permits the easymovement of air around fastener 11. Ambient air can be used to furthercool the fastener, or forced air can provide additional cooling. Asshown schematically in FIG. 1, air amplifiers or air knives 125 can blowforced air in and around the fasteners for still additional cooling.

The final step of the coating process should include the immersion ofthe fasteners in a liquid bath material 128, as contained in receptacle130. The bath material 128 can be water, oil, or another chemical agent.The bath is designed to cool the fastener to a temperature relativelyclose toambient, and can also provide a coating of rust inhibitor on thefastener.

Finally, the fasteners are moved out of the bath by conveyor 135 andmove to another location for storage or packing.

FIG. 7 depicts an exploded view of the preferred embodiment of thenozzle 70 used to spray powdered material such as powder sold under thetrademarkTEFLON® on the fasteners. The preferred nozzle includes acylindrical body portion 172 with a conical end 174. The tip of thenozzle 70 can be asmall outlet 176, or a broader, flatter one as shownin phantom as 178. Inside body portion 172 is a torpedo 180 fordispersing powder. Torpedo 180 is located toward the opening end of body172. After the powder has entered the nozzle at top 184, it movesthrough passageway 187, and then encounters a smaller, cone torpedo 182which is surrounded by annular element 180A projecting from torpedo 180.Cone 182A of cone torpedo 182 thus initially disperses the powder afterit has entered the nozzle at top184 into three slots 186 (only two ofwhich are shown) spaced radially around cone torpedo 182. To acceleratethe powder and prevent clogging of the outlet, a secondary source of airis provided through hose 190 into manifold 192. Preferably, thesecondary air source should be pressurized above the pressure level ofthe incoming powder that is transported by a primary air source. Thissecondary air source assists in providing a steady and even flow ofpowder to and at the output of nozzle 70. This preferred configurationsubstantially eliminates any flutter in the powderoutput and provides animproved, uninterrupted supply of powder which assures an improvedcoating on each fastener.

The secondary air is fed from manifold 192 sealed by 0-rings 193,through passageway 194, out apertures 196, and into the interior chamberdefined by the outside of body portion 172 and conical end 174. Theconfiguration of the apertures can be embodied several ways. Oneembodiment includes apertures 196 spaced approximately 30 degrees oneither side of each slot 186. Other forms could include a series of 12equally spaced apertures 196or a cylindrical manifold, extendinglaterally the complete circumference of nozzle 70 and vertically frommanifold 192 to aperture 196 as now depicted in FIG. 7.

Another desirable feature is to make the nozzle 70 rotatable about anaxis extending from its outlet to its top. Thus, when the nozzle end isconfigured as shown by the flattened outlet 178, the length of the shankportion of the fastener that receives a coating of material can becontrolled. The capability to rotate nozzle 70 approximately 180 degreesis preferred. Vacuum pick-up 72 could be adapted to rotate with nozzle70,or, alternatively, could be made large enough to eliminate the needfor rotation.

The present invention can also be used with liquid coatings, such as theliquid coatings sold by Nylok Fastener Corporation sold under thetrademark PRECOTE®. The fastener is initially heated by an inductioncoil to approximately 150° Fahrenheit, coated, and rotated to obtain auniform 360 degrees coating on the fastener. Heat is applied after theapplication process to dry the coating. Subsequent post coatingoperations are designed to remove the carrier solvent or dispersingmediumfrom the coating.

The method and apparatus of the present invention can be adapted for awidevariety of liquid coating applications. Either gravity or pressurecan be used in applying the coating. Moreover, a broad range ofviscosities of the liquid coating can be accommodated, including wateror solvent based dispersions and/or solutions. These include coatingssuch as a toluene-based coating sold under the trademark PRECOTE® 80 ora water-based coating sold under the trademark PRECOTE® 5.

If it becomes desirable to coat the sides of the head of the fastener,thincaps can be used to cover the otherwise exposed magnet to preventaccumulation of the coating on the magnet 60 and carrying member 52.Such caps can be made of a material such as those sold under thetrademark TEFLON® or any other suitable material. In the same manner asthe caps, a longer adaptive element can slide over a longer part ofcarrying member 52. The adaptive element can have a saddle or clip end,such as clip 75 shown in FIG. 5, that will mechanically hold the head ofa non-ferromagnetic fastener or stud.

Of course, it should be understood that various changes andmodifications to the preferred embodiments described herein will beapparent to those skilled in the art. Such changes and modifications canbe made without departing from the spirit and scope of the presentinvention and without diminishing its attendant advantages. It is,therefore, intended that suchchanges and modifications be covered by thefollowing claims.

What is claimed is:
 1. A method of continuously applying a coatingmaterial to fasteners, comprising:providing a continuous feed line offasteners in which the fasteners are uniformly aligned; moving thefasteners to equally spaced notches on a rotating wheel; transferringthe fasteners from said rotating wheel to a continuous belt withfastener holders that are synchronously alignable with said equallyspaced notches; rotating said continuous belt to advance the fasteners;advancing the fasteners on said belt through a heating station to raisethe temperature of the fasteners above the melting point of the coatingmaterial; applying the coating material to at least a portion of saidfasteners as the fasteners are advancing on said belt; and rotating saidfastener holders during the application of the material.
 2. The methodof claim 1 further comprising the step of cooling said fasteners inambient air after the material is applied.
 3. The method of claim 2further comprising the step of immersing said fasteners in a liquid toprovide further cooling.
 4. The method of claim 2 furthering comprisingthe step of additionally cooling said fasteners with pressurized air. 5.The method of claim 2 further comprising the step of applying a rustinhibitor to said fasteners.
 6. The method of claim 1 further comprisingthe step of collecting and removing material that does not adhere to thefasteners during the application step.
 7. The method of claim 1 whereinsaid fastener holders are magnetic and are rotated at least 360 degreesto coat the entire circumference of said fastener shank portion, saidmagnetic fastener holders properly orienting said fasteners in positionfor coating.
 8. The method of claim 1 whereby said fastener holders aremagnetic and are rotated by engaging a rack of teeth positionedgenerally proximate and parallel to said continuous belt.
 9. The methodof claim 1 further comprising the step of rotating the fasteners aftercoating to achieve a smoother and more even coating finish.
 10. Themethod of claim 1 wherein the coating material is applied with anaccurately adjustable nozzle.
 11. The method of claim 10 wherein saidnozzle is rotated about its own axis to decrease and increase theapplied coating surface area on the shanks of the fasteners.